The present invention relates to nuclear fuel bundles having one or more water rods interconnecting upper and lower tie plates and particularly water rods having capture flanges for capturing one or more spacers to form a structural skeleton for the nuclear fuel bundle.
A typical boiling water nuclear reactor has a reactor core comprised of a plurality of fuel bundles in side-by-side relation to one another. Coolant moderator flows upwardly within the fuel bundles and about the fuel rods within the fuel bundles and is converted to steam to produce power. The fuel rods are located between upper and lower tie plates and are laterally spaced from one another by spacers having openings for receiving the fuel rods and forming a matrix of fuel rods. The spacers are vertically spaced one from the other and may be structurally carried on water rods which transmit water from a lower portion of the fuel bundle for egress into an upper steam vent volume portion of the fuel bundle.
Water rods have also been used to improve moderator distribution by the incorporation of swirl vanes about the water rods. For example, in U.S. Pat. No. 5,229,068, of common assignee herewith, a generally helical extending swirl vane is mounted on a water rod and extends upwardly along the fuel bundle from a location within a spacer and through one or more additional spacers to the upper regions of the fuel bundle. In certain fuel bundles, spacers are sometimes captured between a pair of vertically spaced tabs formed on the water rod. Tabbed water rods, however, lead to difficulties in the fabrication of the fuel bundle. Additionally, oftentimes the spacers and/or fuel rods and water rods are marred or scratched during assembly of the fuel bundle, which can often lead to failure and corrosion of the component part. Accordingly, there is a need to provide a nuclear fuel bundle having one or more water rods which can capture the spacers as well as to distribute the water moderator in the bundle onto the adjacent fuel rods and into the interstices thereof.
In accordance with a preferred embodiment of the present invention, there is provided a water rod constructed in segments having interior passages in communication with one another at adjoining ends for transmitting water along the length of the water rod into the upper regions of the fuel bundle. The water rod segments are sized and configured relative to the openings in the spacers through which the water rod passes to capture the adjoining spacer, precluding substantial movement thereof along the fuel bundle. To accomplish this, the segments of the water rod are provided at adjacent ends thereof with male and female threaded connections, respectively, whereby the water rod can be assembled. The segment ends on opposite sides of the spacer through which the water rod passes have capture flanges which project beyond the peripheral confines of the openings in the spacers through which the water rod extends. Preferably, the capture flanges are in the form of the ends of swirler vanes extending along the outer periphery of the water rod segments between adjacent spacers. Consequently, not only are the spacers captured by the water rod segments but the flow of water about the water rods is directed in a radial direction against the adjacent fuel rods and into the interstices of the adjacent fuel rods.
In a preferred embodiment according to the present invention, there is provided a fuel bundle for a nuclear reactor comprising a plurality of spacers spaced one from the other along the bundle and having a plurality of openings, a plurality of fuel rods extending through the openings in the spacers, at least one water rod extending through a predetermined opening through each of the spacers and generally parallel to the fuel rods, the water rod including first and second water rod segments secured to one another, the segments having interior passages in communication with one another for transmitting fluid along the one water rod, the segments having elements on opposite sides of the one spacer and extending beyond peripheral confines of the predetermined opening for engaging the one spacer between the elements and preventing substantial movement of the spacer along the fuel bundle.
In a further preferred embodiment according to the present invention, there is provided a fuel bundle for a nuclear reactor comprising a plurality of spacers spaced one from the other along the bundle and having a plurality of openings, a plurality of fuel rods extending through the openings in the spacers, at least one water rod extending through a predetermined opening through each of the spacers and generally parallel to the fuel rods, the water rod including first and second water rod segments secured to one another at a joint located within the predetermined opening of one of the spacers, the segments having interior passages in communication with one another at the joint for transmitting fluid along the one water rod, the segments having capture flanges on opposite sides of the one spacer and extending beyond peripheral confines of the predetermined opening for capturing the one spacer between the flanges and preventing substantial movement of the spacer along the fuel bundle.